1. Field of the Invention
The present invention generally relates to personal computers, and more particularly to a pointing device system used in conjunction with portable, laptop or notebook computers.
2. Description of Related Art
Pointing devices are commonly used in conjunction with a computer in order to control the movement of a cursor on a graphics screen. Conventional devices employed for this function are arrow keys on a computer keyboard and computer "mice." Arrow keys typically consist of four adjacent bipolar keys, which move the cursor up, down, left, or right upon depression of a respective key. Such keys are commonly used for editing simple textual applications. However, because the keys must be used sequentially and limit the cursor to orthogonal directions of displacement, arrow keys are impractical to use in many more sophisticated graphical applications.
Computer mice employ mechanical, optical, or other means to control the displacement of a cursor on a graphics screen. The mouse is moved over a flat surface in proportion to the desired motion of the cursor on the graphics screen. While providing the computer user with considerable flexibility over the motion of the cursor on the graphics screen, a computer mouse requires an auxiliary flat surface proximate to the computer keyboard.
With the introduction of small laptop and notebook computers, flexible built-in pointing devices became necessary. Somewhat smaller, more efficient, and more ergonomic devices have been developed that combine the cursor control flexibility of a mouse with the integral keyboard mounting of arrow keys. A variety of these state-of-the-art devices are described in the February 1991 issue of BYTE magazine in an article entitled "Touch-and-Feel Interfaces: Built-In Pointing Devices Replace Mice in Notebooks and Laptops." The devices discussed in this article include trackballs, touchpads, touchscreens, isopoints, and home row keys.
A trackball consists of an upwardly-facing sphere mounted in a specially-designed base that allows the sphere to be freely rotated in any desired direction at any desired velocity. The cursor on the graphics screen is displaced in proportion to the speed and direction at which the sphere is rotated. While trackballs are compact, they require considerable finger movement to produce large cursor displacements at low velocities. In addition, because it is difficult for a system operator to successively rotate the sphere in a constant direction, linearly displacing the cursor on the graphics screen can prove troublesome. Finally, trackballs are not suited for operation in dirty environments because any foreign material deposited on the surface of the sphere can quickly contaminate the internal workings of the unit and thereby impede its operation.
A touchpad consists of an auxiliary rectangular pad whose surface is mapped to correspond to the graphics screen. By touching a location on the touchpad, the computer user directs the computer to move the cursor to the corresponding location on the graphics screen. Touchpads require the computer user to move his/her hand from the keyboard to the touchpad surface in order to displace the cursor on the graphics screen. In addition, because the typical touchpad is considerably smaller than the graphics screen, accurate positioning of the cursor on the graphics screen can prove troublesome. Finally, touchpads only provide control over the cursor's absolute position and do not permit the computer user to direct the cursor's speed or path as it moves from its original to its final position.
A touchscreen is similar to a touchpad except that the system operator interfaces directly with the graphics display by touching the graphics display at a desired location. As with a touchpad, a touchscreen requires the computer user to move his/her hand from the keyboard to the graphics screen in order to displace the cursor. Similarly, touchscreens only provide control over the cursor's absolute position and do not permit the computer user to direct the cursor's speed or path as it moves from its original to its final position.
An isopoint consists of a cylindrical bar that both slides along and revolves about its central axis. The isopoint is typically located on the upwardly-facing surface of the keyboard proximate to the space bar. The computer user slides or revolves the isopoint to generate horizontal or vertical displacement of the cursor on the graphics screen, respectively. As with trackballs, isopoints require considerable finger movement to produce large cursor displacements at low velocities. In addition, a computer user must simultaneously revolve and slide the cylindrical bar to achieve a diagonal displacement of the cursor on the graphics screen, an unnatural and cumbersome operation. Finally, isopoints are not suited for operation in dirty environments because any foreign material deposited on the surface of the cylindrical bar can quickly contaminate the internal workings of the unit and thereby impede its operation.
A home row key consists of a joystick-like mechanism incorporated into a standard keyboard key. Under normal operation, the key simply functions as a bipolar switch to input a particular character. When used in conjunction with another key (such as the CTRL or ALT key), however, the home row key functions as a joystick to displace the cursor on the graphics screen. The displacement of the cursor is governed by the direction in which the key is moved relative to its neutral position and the duration for which the key is held in the non-neutral position. The home row key includes a force sensing mechanism which senses the force and the direction of the applied force. The cursor, in turn, proportionally responds to a force applied.
The home row key has a number of ergonomic disadvantages. Significantly, the home row key necessarily requires the computer user to simultaneously operate two separate keys, an awkward operation. If the user does not correctly enter the key combination, the user will input alpha-numeric characters rather than control the cursor. The user must then delete the characters and then retry the key combination to control the cursor. In addition, because the cursor moves as a function of duration rather than displacement, the computer user cannot quickly move the cursor from one side of the graphics screen to the other. An additional key can be used in conjunction with an home row key to accelerate the cursor's displacement on the graphics screen. However, the use of such a key further complicates the operation of the home row key, requiring yet a third key for the computer user to manipulate. Furthermore, accelerator keys typically increase the speed of the cursor motion incrementally, rather than continuously, limiting the computer user's control over the cursor's displacement.
Moreover, precise positioning of the cursor is difficult because the cursor responds to any application of force applied. That is, the cursor responds to the application of a constant force, of an increasing force and of a decreasing force. Thus, in order to home in on a particular target on the graphic screen, the user must control both the acceleration (resulting from a positive force gradient applied to the home row key) and the deceleration (resulting from a negative force gradient applied to the home row key) of the cursor. Consequently, some users find such a system difficult to operate and constantly "over shoot" a desired target location on the graphic screen.
Furthermore, the small top surface area of the home row key, typically about one square centimeter, provides little tactile feedback with regard to the direction imposed on the cursor. Finally, the home row key requires its own software driver to interface with graphic environments or other application software systems.